Degenerative Muscle Disease - An Overview

Introduction:

When the genes in a human body are interrupted for any reason, they may cause some abnormality or dysfunction. Degenerative muscle disease is one such genetic disease that is a rare condition yet a serious health problem. It is characterized by progressive muscle weakness in the body.

The most common form of degenerative muscle disease is prevalent among young children three to five years old, and one in every 3500 live male births has this disease worldwide. These diseases negatively affect the patient's quality of life and increase the cost of healthcare. Unfortunately, there is no known cure, so prevention is important.

What Is Degenerative Muscle Disease?

Degenerative muscle disease, more commonly known as muscular dystrophy, is a rare genetic disease that causes weakness, degeneration, or deterioration of body muscles. Dystrophy is a Greek word meaning "faulty nourishment." There are more than 30 such genetic diseases.

What Causes Degenerative Muscle Disease?

It is caused by genetic mutations in the human body that affects the protein (required for healthy muscles) production in the body. As these mutations cause changes in the muscle fibers, the functional ability of the muscles deteriorates with time. This increases the disability of the patient, such as unable to walk, difficulty breathing, difficulty swallowing, etc.

Genetic mutations are caused because of the inheritance from the parents. Therefore, the risk of developing the disease must be evaluated if the patient has a family history of muscular dystrophy.

How Does Degenerative Muscle Disease Affect Muscles?

Muscles in the human body are made of fibers that are bonded together with connective tissue. As a result, thousands of muscle fibers are bound together to make one muscle. These muscle fibers' outer layer contains the "dystrophin-glycoprotein complex" protein that prevents muscle damage while contracting and relaxing. When this outer layer is damaged, the protein gets leaked from the muscles, and as a result, muscle fibers become dead and cause degenerative muscle disease.

What Are the Types of Degenerative Muscle Disease?

Various types of degenerative muscle diseases show different symptoms. However, a few common types of degenerative muscle disease are:

1. Duchenne Muscular Dystrophy: It is the most common and severe type. It affects males during early childhood. The life expectancy is usually up to 30 to 40 years. It accounts for 50 % of all degenerative muscle disease cases.

2. Myotonic Muscular Dystrophy: It is also called Steinert’s disease and may occur at any stage of life. It may or may not decrease life expectancy. The patient generally shows a slow progression of disability. It affects both men and women of any age.

3. Becker Muscular Dystrophy: It is similar to Duchenne muscular dystrophy but is less severe and occurs in the later stages of childhood.

4. Facioscapulohumeral Muscular Dystrophy: It is the third most common disease; it may occur in children or adults; is less severe with slow progression. It initially affects the muscles of the face, shoulder, and upper arms. It is also called Landouzy-Dejerine disease.

5. Limb-girdle Muscular Dystrophy: It develops between the teenage years and early adulthood. It is a group of more than 20 genetic conditions and mainly affects shoulder and hip muscles.

6. Emery Dreifuss Muscular Dystrophy: It mainly affects males of young age, usually ten years of age, but symptoms appear in their late twenties. It affects the muscles of the upper arm and lower leg.

7. Oculopharyngeal Muscular Dystrophy: It usually occurs among older adults aged 50 to 60 years. It affects facial, leg, and throat muscles, causing difficulty swallowing.

Types of Degenerative Muscle Diseases and Age of Occurrence:

• Duchenne muscular dystrophy: 2 to 6 years.

• Myotonic muscular dystrophy: 20 to 40 years.

• Becker muscular dystrophy: Teenage to young adults.

• Facioscapulohumeral muscular dystrophy: Childhood to young adults.

• Limb-girdle muscular dystrophy: Late childhood to middle age.

• Emery Dreifuss muscular dystrophy: Childhood to teenage.

• Oculopharyngeal muscular dystrophy: 50 to 60 years.

What Are the Signs and Symptoms of Degenerative Muscle Disease?

Every degenerative muscle disease type has its own set of signs and symptoms. Mainly muscle weakness is the major symptom of every type. Different parts and muscles of the body get affected depending on the type of dystrophy. A few common signs and symptoms are:

• Enlarged muscles of the calf (muscles on the back of the lower leg).

• Difficulty in walking.

• Difficulty in swallowing.

• Heart problems such as heart failure.

• Stiffness or looseness in joints.

• Pain in muscles.

• A problem with breathing.

How Are Degenerative Muscle Diseases Diagnosed?

Different diagnostic methods are used for different degenerative muscle diseases. The choice of the diagnostic method also depends on the patient's age and the onset of the signs and symptoms. The commonly used diagnostic methods are:

• Patient’s Family Medical History: The doctor takes family history to know the cause or source of the disease, such as inheritance or other underlying conditions.

• Diagnostic Tests: Blood and urine tests are done to detect the gene defect and identify the type of dystrophy present.

• Exercise Test: Patients are asked to do a few exercises, such as breathing exercises, that help the doctor identify the type of disease and muscle strength.

• Genetic Tests: Patients' Genes are tested to identify the cause of the disease. The genes are tested through various tests such as enzyme analysis, genetic linkage, whole-genome sequencing, etc.

• Imaging Tests: It is done to examine the quality of muscles, identify any abnormalities present, and monitor the disease progression. Magnetic resonance imaging is a commonly used test.

• Biopsy: A small sample of the diseased muscle (biopsy) is taken to monitor the effectiveness of the treatment and for further diagnosis.

• Immunofluorescence: It is done to detect muscle proteins, such as dystrophin protein in muscle fibers.

• Electric Tests of the Nerves: It is done to identify the physical and chemical changes in the nervous system.

How Are Degenerative Muscle Diseases Treated?

As degenerative muscle diseases are genetic, they cannot be treated or cured completely; only the symptoms can be treated. Therefore, it may include various combinations of the treatment therapies such as physical therapy, medications, and surgical procedures. In general, the treatment options are mentioned below:

1. Ventilation: Assisted ventilation may be required in later stages to provide supplemental oxygen to the patient if the respiratory system muscles are diseased and cause difficulty breathing.

2. Medications: Few medicines are prescribed to delay the process of degeneration of muscles. For example, injections of Golodirsen and Viltolarsen are given to treat Duchenne muscular dystrophy, and corticosteroids such as prednisolone are also prescribed to slow down the rate of degeneration. Muscle relaxers for degenerative muscle diseases are prescribed to relieve muscle spasms.

3. Physical Therapy: It helps to maintain muscle flexibility, improve movement and prevent deformities. For example, stretching, posture correction exercise, regular moderate exercise, etc.

4. Speech Therapy: It may help patients whose facial muscles are diseased.

5. Surgery: It is done to ease the complications of degenerative muscle diseases. For example, tendon or muscle release surgery, pacemaker to treat heart problems, cataract surgery, etc.

Conclusion:

Degenerative muscle diseases are rare genetic diseases, more commonly seen in young males leading to serious health issues such as heart failure and death. Although the treatment is still not known, symptoms can be managed to slow down muscle deterioration.